DNA from fly puparia?

We are interested in extracting DNA from fly puparia ('the pupal case').
They are about the size of house flies.
Alternatively, we need to extract enough DNA for PCR from the flies
without excessively harming them prior to releasing them.
I would appreciate any protocols or stories of success or failure-
Thank you,
Dave Carmean
Biological Sciences
Simon Fraser University
carmean at sfu.ca